Mirror for astronomical purposes



Jan.' 22, 1935. 1,988,952

MI RROR FOR ASTRONOMICAL PURPOSES Filed June 29, 1932 in van for:

Patented Jan.22,1935 A I v 1383352 UNITED STATES PATENT OFFICE MIRROR. FOB ASTRONOMICAL PURPOSES Franz Meyer, Jena, Germany, assignor to the firm Carl Zeiss, Jena, Germany Application June 29, 1932, Serial No. 619,941 In Germany July 8, .1931

'2.Claims. (Cl. 88-1) I have filed an application in Germany, July 8, body and can be cemented thereto. The sagged 1931. disc exactly corresponding to the form of the mir- Mirrors for astronomical purposes are generror body, the agglutinant between disc and mir- 'ally made of glass. when great dimensions are ror body is of uniformthickness throughout and required, the manufacture of tensionless glasses will not distort the disc. 5

is rather diflicult and costly. Composing a mir- The'accompanying drawing illustrates the inror of several pieces-is hardly practicable with vention by way of an example; Figures 1 and 2 glass, since cementing will greatly curtail the show a concave mirror in a plan view and in a life of the mirror and the brittleness of the glass section through line 2-2 in Figure 1, respectively.

' is prohibitive to the use of screws and the like. The example represented in the drawing is a 10 According to the invention, mirrors of comparaceramic mirror body consisting of a central part tively great dimensions are made of a body conand six peripheral parts; The central part consisting of several pieces of ceramic material, for sists of a spherical upper part 9 which is coninstance of porcelain, each of these pieces, or nected below to ribs 9 Each of the peripheral the body in its entirety, being connected to a parts consists of'a'spherical upper part i which 15 sheet of a polishable substance, for instance is connected below to ribs 1?. The peripheral glass. This connexion is effected by fusing or agparts are connected to each other and to the cenglutinating the said pieces, or the whole body, tral part by means of screws 7'. The upper surto the said sheet. To compose the said body'of faces of all seven parts are so ground that the several pieces is possible, since it is easily pracbody consisting of these partshas approximately 20 ticable with ceramic material to use screws and the form which the completed mirror is to have. the like for permanently holding the different The mirror body having been u d, t is pieces in their correct positions relatively to ered by means of a glass disc is, whereupon the each other. The-great resistance achieved with said body and disc are heated to such an extent 5 ceramic material also oifers the advantage of that the disc It softens and sags on the mirror '25 making a mirror ,body consisting of one or sevbody. When cooled down, the disc is is removed eral pieces comparatively thin and, if so required, from the mirror body-and subsequently connect-' of having it ribbed. Amirror constructedinthis ed to the same by means of an agglutinant. manner is very advantageous, especially because Grinding and polishing of the upper surface of it reacts-comparatively quickly upon changes of thedisc k is effected after the said agglutination 30 temperature, reassuming as it does its original as been eflected. form after any such change of temperature. I claim: A comparatively thin cover, as may be pro- 1. A mirror for astronomical purposes, conduced for instance by glazing, requires the ceramsisting of a body of ceramic material, the body to body to have at the outset the exact finally being Composed o a plurality of P means 3 required form. To achieve this is rather diflicult, t nn e t s parts, and a li t-r fl tiv the more so as-slight distortions 'of the ceramic glass disc connected to the said body. bodycannot be avoided when this body is heated 2. A method for manufacturing a mirror for a during the glazing process. For this reason it is astronomical purposes, consisting in providing a 40 more convenient to make the polishable cover so body of ceramic material with a surface of ap- 40 thick that it may be treated subsequently, the proximately the form which the completed mir ceramic body therefore not requiring to be formed ror is to have, in placing a glass disc on the body, 11;]; great. a uracy; The difficulties caused by in heating the said body and disc to such an exfusing the glass on the said body are nevertheless tent that the disc sags on the body, in removing considerable. They may be avoided by-cementthe disc, when having cooled down, from the body 45 ing to the prepared surface of the mirror body and in subsequently connecting this disc tothe a glass disc conforming to the same. Also when said body by means of 'ag'glutinant,- and in this surface is vaulted can the said disc easily grinding and polishing the glass disc so as to give be made to conform to the surface, namelyby it the finally required form. softening it above the mirror body to such an extent that it sags and assumes the shape of this FRANZ MEYER. 

